1. Field of the Invention
The present invention relates to a clutch wheel for a timepiece.
2. Description of the prior Art
The conventional clutch wheel manufactured by machining a metal is formed, as shown in FIG. 4, with a cylindrical portion 50 in a center and a plurality of clutch teeth 51 radially provided from an outer surface of the cylindrical portion 50. The cylindrical portion is provided, in an inner peripheral surface, with a convex portion 52 and a concave portion 53 and formed such that a hand setting stem (not-shown) having convex and concave portions in an outer peripheral surface penetrates axially slidable and relatively non-rotatable. In particular, an opening defined by the inner peripheral surface of the cylindrical portion has a surface matching an outer peripheral surface of the hand setting stem of the timepiece so that the two rotate as a unit.
In a state the hand setting stem is drawn out by one stage, a wheel train is corrected for rotation angle (hand-rotation correction). That is, in the state the hand setting stem is drawn by one stage, a hand-setting-stem convex-and-concave portion and a convex-and-concave portion of the clutch wheel become engaged so that the clutch wheel rotates along with rotation of the hand setting stem. The clutch wheel is formed with a plurality of clutch teeth to mesh with setting teeth of the setting wheel to deliver rotational motion to the setting wheel. The rotating setting wheel performs hand-rotation correction through the wheel train. In hand-rotation correction, gears are generally meshed in the order of the clutch wheelxe2x86x92the setting wheelxe2x86x92a minute gearxe2x86x92a minute indicator wheel mounting a slip mechanism, a minute pinionxe2x86x92hour indicator wheel, thereby performing hand-rotation correction.
The conventional clutch wheel as above has the following problems:
(1) If hand-rotation correction as described above is repeatedly performed, the clutch wheel manufactured by machining a metal has a load concentration at a base end of the clutch teeth, and clutch teeth become broken and the wheel goes out of engagement with the setting wheel, disabling hand-rotation correction.
Meanwhile, if the clutch tooth base is increased in thickness, the strength improves but the spacing between the teeth become narrow. Accordingly, the clearance with the setting wheel decreases thereby stretching the clutch tooth and the setting tooth against one another and improper meshing.
(2) Because there is in the under no receiving surface upon being forged, manufacture is only by machining resulting in expensive cost.
It is a first object of the present invention to eliminate the above problems of the prior art and provide a clutch wheel that has a clutch teeth high in strength and less liable to be broken and is inexpensive in manufacture cost.
It is a second object of the invention to provide a timepiece clutch that has clutch teeth having a strength equivalent to or higher than the conventional clutch but cheap in manufacture cost.
In accordance first with a aspect of the present invention for solving the first problem described above is a clutch wheel for a timepiece formed of a metal, and comprising a cylindrical portion in which a hand setting stem penetrates slidably and relatively non-rotatably, a flange portion integrally formed with a base end of the cylindrical portion, a plurality of teeth integrally formed on a side surface of the flange portion and radially formed in a manner surrounding the cylindrical portion from an outer peripheral surface of the cylindrical portion.
A second aspect of the invention for serving the second problem described above is a clutch wheel for a timepiece formed of a metal, and comprising a cylindrical portion in which a hand setting stem penetrates slidably and relatively non-rotatably, a flange portion integrally formed with a base end of the cylindrical portion, a plurality of individual teeth integrally formed on a side surface of the flange portion and radially formed in a manner surrounding the cylindrical portion spaced from an outer peripheral surface of the cylindrical portion.
A third aspect of the present invention for solving the second problem described above is a clutch wheel for a timepiece in which the individual teeth have a cylindrical shape.
(Operation)
If forming as in the first form, even if hand-rotation correction is repeatedly performed, the load is distributed not only in a base of the clutch teeth at the outer peripheral surface of the cylindrical portion but also in a base of the clutch teeth to the flange side surface, making breaking less likely to occur. Also, because forging, die may include a type separated into two parts in an upper level of the flange due to the provision of the flange portion, it is possible to manufacture by forging a metal and to thereby reduce manufacture cost and lead time as compared to those associated with clutches manufactured by machining.
Furthermore, because of provision of the flange integrally formed with the base end of the cylindrical portion, the strength of the entire clutch wheel including the clutch teeth improves.
If the clutch wheel is structured as in the second or the third aspects, manufacture by forging is made possible as mentioned before and manufacture cost can be reduced.
Furthermore, because the flange portion is provided that is integrally formed with the base end of the cylindrical portion, the strength of the entire clutch wheel improves with the strength of the clutch teeth kept equal to or higher than the conventional.